The dispensing of compressed gas from compressed gas storage systems to lower-pressure receiving vessels is known in the art for various applications such as supplying fuel to compressed natural gas (CNG)-powered or hydrogen-powered vehicles. A compressed gas storage system typically comprises multiple high-pressure gas storage volumes with a piping and valve system to dispense gas to the lower-pressure receiving vessel sequentially from each of the high-pressure gas storage volumes and a gas supply system to refill the gas storage volumes after dispensing is complete. A storage volume may comprise a single vessel or a bank of vessels.
Typical dispensing processes that transfer gas sequentially from each of the compressed gas storage volumes to lower-pressure receiving vessels are known in the art as cascade dispensing processes. Examples of cascade dispensing processes are disclosed in U.S. Pat. Nos. 5,406,988, 5,673,735, 6,779,568 B2, and 7,128,103 B2, and U.S. Patent Application Publication Nos. 2003/0175564 A1, 2006/0260950A1, and 2007/0125441 A1.
In a cascade process, the lower-pressure receiving vessel is filled at increasing pressures from each of a plurality of compressed gas storage volumes in sequence wherein each gas storage volume operates within a given pressure range for each fill step. For example, in a system with three compressed gas storage volumes each containing gas at an upper gas storage pressure, a first gas storage volume dispenses gas to the receiving vessel from an initial pressure to a first intermediate pressure, a second storage volume dispenses gas to the receiving vessel from the first intermediate pressure to a second intermediate pressure, and a third storage volume dispenses gas to the receiving vessel from the second intermediate pressure to a final fill pressure. The storage volumes are refilled from a gas source to the upper gas storage pressure, and gas is dispensed subsequently to another lower-pressure receiving vessel in the same manner. In each subsequent dispensing step, therefore, the first gas storage volume always dispenses gas in a lower pressure range, the second storage volume always dispenses gas in an intermediate pressure range, and the third storage volume always dispenses gas in a higher pressure range.
The use of cascade gas dispensing systems will grow substantially with the anticipated growth in the number of compressed gas-fueled motor vehicles in coming years. Improvements in the design and operation of cascade gas dispensing systems will be needed to ensure efficient operation and upper operating life of future cascade gas dispensing systems. This need is addressed by the aspects of the invention described below and defined by the claims that follow.